The field of the invention is a heat exchanger for furnaces and heaters, including hot air furnaces, heating boilers, and water heaters, more particularly a heat exchanger having an automatic damper control which cyclically retains heated gases for a short period in each flue to allow additional time for transfer of heat before discharging the gases into a smokepipe and thence to a chimney.
The prior art for increasing the efficiency of the heat transfer includes devices to increase the length of travel of the heated gases and the fluid to be heated such as in Jury U.S. Pat. No. 3,926,173; and devices to recover heat from the gases after they have passed into the smokepipe, such as Anable U.S. Pat. No. 3,930,489. Increasing the length of travel of the gases through the heat transfer part of the heater, as in the Jury U.S. Pat. No. 3,926,173 increases the bulk of the heater and interferes with its ability to vent by natural draft even the fumes of a pilot flame. In this invention the objective of heat transfer efficiency is obtained with little or no increase in bulk and the natural draft venting ability of the heater is unimpaired. There is not always room for the smoke pipe heat recovery units, such as Anable U.S. Pat. No. 3,930,489, in cases where the heater is close to the chimney and space is limited. The present invention however is useful in such limited space. It is a new and useful means for recovering more heat from the burning of fuel and thus conserving energy. Another feature of the heater is that the flues taper to a larger width at exit. This taper causes more particles of the air to be heated to wipe against a wall of the flue when rising, thus improving heat transfer. Prior art achieves this objective with sinuous flues which impair natural draft.